Secondary alkanolamines associated with an alkyl group are potentially attractive post-combustion CO2-capturing solvents. Their reactivity with CO2 is influenced by the nature of the alkyl group that substitutes the hydrogen atom of the amino functional group. In the present work, we measured the rates of CO2 absorption into aqueous solutions of n-propylmonoethanolamine (PMEA) and n-butylmonoethanolamine (BMEA) in a stirred-cell reactor under fast pseudo-first-order conditions. The concentrations of PMEA and BMEA in the water solutions were changed in the 2-3 kmol m(-3) range. It was discovered that, unlike the;usual amines, PMEA and BMEA followed overall third-order kinetics. We evaluated the reaction rate constants at different temperatures, viz., 303, 308, and 313 K, and discovered that PMEA reacts with CO, faster than BMFA. Furthermore, we gave an interpretation of the kinetic data using the zwitterion and termolecular mechanisms. Finally, a comparison of the efficacy of the investigated solvents with N-methylmonoethanolamine (MMEA) and N-ethylmonoethanolamine (EMEA) was accomplished. It was found that reactivity of amines diminished in the order EMEA > MMEA > PMEA > BMEA.